Economic Growth David Weil 2nd Edition

Working Through the Weights: How to Actually Use Weil's Textbook

I picked up the David Weil second edition because my department required it for a graduate-level macro course. The book itself is solid. The real challenge isn't reading it — it's actually doing the exercises in a way that doesn't leave you going in circles. A lot of students breeze through the Solow chapters without truly understanding the transition dynamics, then hit a wall when the problem sets start asking for steady-state comparisons across different parameter values. I've been around that block enough times to know what trips people up. What makes this edition different from the first is the expanded treatment of endogenous growth and the slightly more rigorous treatment of cross-country growth regressions. The production function chapters are clearer, but the exercise sets are where most students struggle. Let me walk through how I approached it. Start with Chapter 2, the Solow model. Don't just read the derivation. The book gives you the capital accumulation equation, but it skips over the intuition for why the golden rule saving rate matters in empirical work. I used to skip ahead when I was an undergrad, and it cost me on the midterm. The key insight most people miss is that the steady state isn't where you want to be if you're maximizing consumption per worker. The golden rule saving rate is s = alpha, where alpha is the capital share. That's it. Simple. The book states it clearly, but it takes a while to click.

When you get to Chapter 4 on cross-country growth, pay attention to the Barro-type regressions. Weil walks through the data issues carefully, which is rare for an introductory text. Most books gloss over measurement error in initial income and just present the results as gospel. The second edition does better here, but it still takes a second read to catch everything.

Working the Exercise Sets Without Losing Your Mind

Here's the practical part. The end-of-chapter problems in Weil are not trivial. They require you to actually manipulate the equations, not just plug numbers in. I spent probably three weeks on the first six chapters doing problems at a pace that felt slow, but it saved me later when the course kicked into gear. For the Solow model problems, here's what works. Write out the production function in per-capita terms first. Y/L = f(K/L). Then take the time derivative and set it equal to zero for the steady state. This seems obvious, but I lost points in grad school for skipping this step and assuming I knew the steady-state capital stock by heart. You don't. The numbers change depending on population growth, depreciation, and the production function parameters. The most useful trick I found for the exercise sets involves setting up a small spreadsheet. I used Excel for most of the numerical problems, and it cut my time in half. Define cells for s, n, delta, alpha, and A. Put the steady-state formula for k* in a cell as (s*A/(n+delta))^(1/(1-alpha)). Then for transition dynamics, iterate using k_{t+1} = s*A*k_t^alpha + (1-delta)*k_t. This took me about ten minutes to set up the first time, and it paid for itself within two days.

Where Students Get Stuck and How to Get Unstuck

The biggest stumbling block is the distinction between growth accounting and growth theory. Weil covers both, and they're easy to confuse. Growth accounting asks: how much of observed output growth is explained by capital accumulation versus technology? Growth theory asks: what determines the long-run growth rate? Most students treat these as the same question. They're not. Another issue I ran into regularly was misinterpreting the role of the production function assumptions. The Cobb-Douglas form is used throughout the book, and it's mathematically convenient, but it has a limitation that Weil mentions only briefly. The elasticity of substitution between capital and labor is fixed at one. In the data, this isn't always true. When I ran into this in a research project, I tried extending the model to a constant elasticity of substitution production function, and the steady-state analysis became considerably messier. Not impossible, but you should know you're leaving the standard framework. The human capital chapter (Chapter 9 in most printings) is also where the book gets dense. Weil introduces the idea that part of what we attribute to physical capital accumulation might really be human capital accumulation. The Mankiw-Romer-Weil three-sector model shows up here. The algebra is manageable, but the intuition requires you to think about education and training as investment, not consumption. I found that drawing the phase diagram for the extended model helped more than re-reading the prose three times.

What the Book Doesn't Cover Well Enough

No textbook is complete. Weil's second edition is strong on the neoclassical and endogenous growth frameworks, but it doesn't spend much time on recent developments in the macroeconomics of growth. Things like the role of financial frictions in growth, or the newer work on inequality and growth dynamics, get short shrift. If you're doing independent research, you'll need to supplement with journal articles. The treatment of empirical evidence is also somewhat dated in places. The cross-country regression results presented in the book reflect data and methods from the late 1990s and early 2000s. Since then, there's been important work on the robustness of these findings, including papers by Rodrik, Subramanian, and Trebbi that question how much of the growth-institution correlation survives when you control for geography and trade costs. Weil acknowledges some of this, but the second edition doesn't go deep enough for someone who wants to engage with the current debate. One more practical note. If you're working through the book on your own, don't skip the appendix material. The math review sections are useful even if you think you're comfortable with calculus. I wish I'd actually read those before attempting the optimization problems in the later chapters. The Lagrangian derivations assume you're comfortable with first-order conditions, and if you're rusty, you'll waste time there.

A Real Problem I Hit and How I Fixed It

During a teaching assistantship, I had a student who couldn't get the numerical answer for a problem involving convergence speed in the Solow model. The issue was that the book uses continuous time notation in some places and discrete time in others, and the student was mixing the two. The convergence speed parameter is lambda = (1-alpha)*(n+g+delta) in continuous time, but in discrete time it's 1 - (1-delta)^{(1-alpha)}, approximately. I had her write out both forms side by side, pick one and stick with it for the entire problem set, and redo the calculation. She got the right answer on the second try. It sounds minor, but notation inconsistency is a surprisingly common source of errors in this book. If you want a supplemental resource, the companion solutions manual helps, but it's not essential. The real value comes from working through the problems yourself and checking your algebra step by step. Weil's explanations are clear enough that you don't need a secondary text unless you're struggling with the mathematical foundations. In that case, look at Romer's Advanced Macroeconomics for a more rigorous treatment, though it's a heavier read. The second edition is worth the time. It's not the most exhaustive growth textbook available, but it's one of the most readable ones, and the problem sets are designed to make you actually do the work rather than just absorb the theory passively. That's the main thing I'd emphasize. Read it actively. Work the problems. Set up the spreadsheets. The material will stick better that way.